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 $93.78   5.263%   $98.7156   $98.72   $98.70   $98.70  
  Purchase #2 $43.48   5.466%   $45.8566   $45.86   $45.85   $45.90  
  Purchase #3 $205.59   8.447%   $222.9562   $222.96   $222.95   $223.00  
  Purchase #4 $243.48   9.282%   $266.0798   $266.08   $266.10   $266.10  
  Purchase #5 $39.51   12.512%   $44.4535   $44.45   $44.45   $44.50  
  Purchase #6 $155.46   7.580%   $167.2439   $167.24   $167.25   $167.20  
  Purchase #7 $236.97   3.826%   $246.0365   $246.04   $246.05   $246.00  
  7 purchase totals = $1,018.27       $1,091.3421   $1,091.35   $1,091.35   $1,091.40