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 $137.78   10.290%   $151.9576   $151.96   $151.95   $152.00  
  Purchase #2 $96.60   5.547%   $101.9584   $101.96   $101.95   $102.00  
  Purchase #3 $165.92   13.605%   $188.4934   $188.49   $188.50   $188.50  
  Purchase #4 $246.52   10.701%   $272.9001   $272.90   $272.90   $272.90  
  Purchase #5 $239.75   6.296%   $254.8447   $254.84   $254.85   $254.80  
  Purchase #6 $46.71   12.128%   $52.375   $52.38   $52.40   $52.40  
  Purchase #7 $147.33   11.566%   $164.3702   $164.37   $164.35   $164.40  
  7 purchase totals = $1,080.61       $1,186.8994   $1,186.90   $1,186.90   $1,187.00