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 $132.58   13.714%   $150.762   $150.76   $150.75   $150.80  
  Purchase #2 $86.34   10.341%   $95.2684   $95.27   $95.25   $95.30  
  Purchase #3 $84.91   13.155%   $96.0799   $96.08   $96.10   $96.10  
  Purchase #4 $49.73   8.163%   $53.7895   $53.79   $53.80   $53.80  
  Purchase #5 $232.61   10.671%   $257.4318   $257.43   $257.45   $257.40  
  Purchase #6 $246.33   3.600%   $255.1979   $255.20   $255.20   $255.20  
  Purchase #7 $219.70   10.723%   $243.2584   $243.26   $243.25   $243.30  
  7 purchase totals = $1,052.20       $1,151.7879   $1,151.79   $1,151.80   $1,151.90