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 $202.76   6.532%   $216.0043   $216.00   $216.00   $216.00  
  Purchase #2 $58.45   11.771%   $65.3301   $65.33   $65.35   $65.30  
  Purchase #3 $239.36   3.203%   $247.0267   $247.03   $247.05   $247.00  
  Purchase #4 $225.40   12.725%   $254.0822   $254.08   $254.10   $254.10  
  Purchase #5 $144.98   7.123%   $155.3069   $155.31   $155.30   $155.30  
  Purchase #6 $134.77   7.870%   $145.3764   $145.38   $145.40   $145.40  
  Purchase #7 $179.79   11.456%   $200.3867   $200.39   $200.40   $200.40  
  7 purchase totals = $1,185.51       $1,283.5133   $1,283.52   $1,283.60   $1,283.50