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 $221.84   5.184%   $233.3402   $233.34   $233.35   $233.30  
  Purchase #2 $115.48   6.282%   $122.7345   $122.73   $122.75   $122.70  
  Purchase #3 $160.60   8.342%   $173.9973   $174.00   $174.00   $174.00  
  Purchase #4 $250.32   11.562%   $279.262   $279.26   $279.25   $279.30  
  Purchase #5 $116.82   5.744%   $123.5301   $123.53   $123.55   $123.50  
  Purchase #6 $235.56   11.685%   $263.0852   $263.09   $263.10   $263.10  
  Purchase #7 $63.62   6.216%   $67.5746   $67.57   $67.55   $67.60  
  7 purchase totals = $1,164.24       $1,263.5239   $1,263.52   $1,263.55   $1,263.50