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 $243.89   12.801%   $275.1104   $275.11   $275.10   $275.10  
  Purchase #2 $63.91   6.331%   $67.9561   $67.96   $67.95   $68.00  
  Purchase #3 $212.98   4.849%   $223.3074   $223.31   $223.30   $223.30  
  Purchase #4 $25.98   6.688%   $27.7175   $27.72   $27.70   $27.70  
  Purchase #5 $203.30   6.513%   $216.5409   $216.54   $216.55   $216.50  
  Purchase #6 $189.70   13.184%   $214.71   $214.71   $214.70   $214.70  
  Purchase #7 $154.85   5.117%   $162.7737   $162.77   $162.75   $162.80  
  7 purchase totals = $1,094.61       $1,188.1160   $1,188.12   $1,188.05   $1,188.10