Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $55.34   13.282%   $62.6903   $62.69   $62.70   $62.70  
  Purchase #2 $131.35   13.582%   $149.19   $149.19   $149.20   $149.20  
  Purchase #3 $247.79   8.721%   $269.3998   $269.40   $269.40   $269.40  
  Purchase #4 $149.47   10.607%   $165.3243   $165.32   $165.30   $165.30  
  Purchase #5 $94.38   9.615%   $103.4546   $103.45   $103.45   $103.50  
  Purchase #6 $238.30   12.700%   $268.5641   $268.56   $268.55   $268.60  
  Purchase #7 $117.91   13.146%   $133.4104   $133.41   $133.40   $133.40  
  7 purchase totals = $1,034.54       $1,152.0335   $1,152.02   $1,152.00   $1,152.10