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 $120.96   11.212%   $134.522   $134.52   $134.50   $134.50  
  Purchase #2 $54.30   8.474%   $58.9014   $58.90   $58.90   $58.90  
  Purchase #3 $193.62   8.715%   $210.494   $210.49   $210.50   $210.50  
  Purchase #4 $164.58   7.235%   $176.4874   $176.49   $176.50   $176.50  
  Purchase #5 $61.41   7.555%   $66.0495   $66.05   $66.05   $66.00  
  Purchase #6 $167.26   8.457%   $181.4052   $181.41   $181.40   $181.40  
  Purchase #7 $209.37   11.266%   $232.9576   $232.96   $232.95   $233.00  
  7 purchase totals = $971.50       $1,060.8171   $1,060.82   $1,060.80   $1,060.80