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 $52.85   5.494%   $55.7536   $55.75   $55.75   $55.80  
  Purchase #2 $224.83   6.781%   $240.0757   $240.08   $240.10   $240.10  
  Purchase #3 $228.70   13.813%   $260.2903   $260.29   $260.30   $260.30  
  Purchase #4 $231.52   9.287%   $253.0213   $253.02   $253.00   $253.00  
  Purchase #5 $85.93   7.418%   $92.3043   $92.30   $92.30   $92.30  
  Purchase #6 $61.62   5.829%   $65.2118   $65.21   $65.20   $65.20  
  Purchase #7 $189.72   6.502%   $202.0556   $202.06   $202.05   $202.10  
  7 purchase totals = $1,075.17       $1,168.7126   $1,168.71   $1,168.70   $1,168.80