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 $85.94   11.471%   $95.7982   $95.80   $95.80   $95.80  
  Purchase #2 $198.72   6.191%   $211.0228   $211.02   $211.00   $211.00  
  Purchase #3 $86.30   6.265%   $91.7067   $91.71   $91.70   $91.70  
  Purchase #4 $24.46   8.419%   $26.5193   $26.52   $26.50   $26.50  
  Purchase #5 $219.30   12.584%   $246.8967   $246.90   $246.90   $246.90  
  Purchase #6 $156.27   9.345%   $170.8734   $170.87   $170.85   $170.90  
  Purchase #7 $43.60   12.284%   $48.9558   $48.96   $48.95   $49.00  
  7 purchase totals = $814.59       $891.7729   $891.78   $891.70   $891.80