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 $36.51   13.184%   $41.3235   $41.32   $41.30   $41.30  
  Purchase #2 $65.98   3.722%   $68.4358   $68.44   $68.45   $68.40  
  Purchase #3 $149.87   11.685%   $167.3823   $167.38   $167.40   $167.40  
  Purchase #4 $132.72   12.625%   $149.4759   $149.48   $149.50   $149.50  
  Purchase #5 $223.55   9.736%   $245.3148   $245.31   $245.30   $245.30  
  Purchase #6 $192.35   10.378%   $212.3121   $212.31   $212.30   $212.30  
  Purchase #7 $150.88   7.376%   $162.0089   $162.01   $162.00   $162.00  
  7 purchase totals = $951.86       $1,046.2533   $1,046.25   $1,046.25   $1,046.20