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 $87.97   5.488%   $92.7978   $92.80   $92.80   $92.80  
  Purchase #2 $200.52   11.354%   $223.287   $223.29   $223.30   $223.30  
  Purchase #3 $225.34   3.370%   $232.934   $232.93   $232.95   $232.90  
  Purchase #4 $177.30   3.760%   $183.9665   $183.97   $183.95   $184.00  
  Purchase #5 $29.29   9.704%   $32.1323   $32.13   $32.15   $32.10  
  Purchase #6 $182.63   10.503%   $201.8116   $201.81   $201.80   $201.80  
  Purchase #7 $82.79   8.574%   $89.8884   $89.89   $89.90   $89.90  
  7 purchase totals = $985.84       $1,056.8176   $1,056.82   $1,056.85   $1,056.80