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 $152.53   11.191%   $169.5996   $169.60   $169.60   $169.60  
  Purchase #2 $30.67   5.444%   $32.3397   $32.34   $32.35   $32.30  
  Purchase #3 $177.72   13.417%   $201.5647   $201.56   $201.55   $201.60  
  Purchase #4 $232.32   11.836%   $259.8174   $259.82   $259.80   $259.80  
  Purchase #5 $201.33   13.809%   $229.1317   $229.13   $229.15   $229.10  
  Purchase #6 $56.87   7.261%   $60.9993   $61.00   $61.00   $61.00  
  Purchase #7 $45.41   13.742%   $51.6502   $51.65   $51.65   $51.70  
  7 purchase totals = $896.85       $1,005.1026   $1,005.10   $1,005.10   $1,005.10