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 $142.99   6.483%   $152.26   $152.26   $152.25   $152.30  
  Purchase #2 $205.54   6.380%   $218.6535   $218.65   $218.65   $218.70  
  Purchase #3 $41.57   7.755%   $44.7938   $44.79   $44.80   $44.80  
  Purchase #4 $222.98   12.819%   $251.5638   $251.56   $251.55   $251.60  
  Purchase #5 $94.57   9.180%   $103.2515   $103.25   $103.25   $103.30  
  Purchase #6 $110.64   9.732%   $121.4075   $121.41   $121.40   $121.40  
  Purchase #7 $9.99   9.517%   $10.9407   $10.94   $10.95   $10.90  
  7 purchase totals = $828.28       $902.8708   $902.86   $902.85   $903.00