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 $68.95   8.713%   $74.9576   $74.96   $74.95   $75.00  
  Purchase #2 $144.70   6.504%   $154.1113   $154.11   $154.10   $154.10  
  Purchase #3 $176.52   11.454%   $196.7386   $196.74   $196.75   $196.70  
  Purchase #4 $223.97   8.329%   $242.6245   $242.62   $242.60   $242.60  
  Purchase #5 $24.31   4.842%   $25.4871   $25.49   $25.50   $25.50  
  Purchase #6 $179.92   12.156%   $201.7911   $201.79   $201.80   $201.80  
  Purchase #7 $29.48   7.281%   $31.6264   $31.63   $31.65   $31.60  
  7 purchase totals = $847.85       $927.3366   $927.34   $927.35   $927.30