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 $89.61   5.114%   $94.1927   $94.19   $94.20   $94.20  
  Purchase #2 $177.39   13.719%   $201.7261   $201.73   $201.75   $201.70  
  Purchase #3 $129.41   12.303%   $145.3313   $145.33   $145.35   $145.30  
  Purchase #4 $197.58   3.120%   $203.7445   $203.74   $203.75   $203.70  
  Purchase #5 $127.49   8.329%   $138.1086   $138.11   $138.10   $138.10  
  Purchase #6 $88.62   6.406%   $94.297   $94.30   $94.30   $94.30  
  Purchase #7 $86.72   9.134%   $94.641   $94.64   $94.65   $94.60  
  7 purchase totals = $896.82       $972.0412   $972.04   $972.10   $971.90