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 $14.87   12.464%   $16.7234   $16.72   $16.70   $16.70  
  Purchase #2 $136.87   10.120%   $150.7212   $150.72   $150.70   $150.70  
  Purchase #3 $27.50   5.578%   $29.034   $29.03   $29.05   $29.00  
  Purchase #4 $184.68   9.826%   $202.8267   $202.83   $202.85   $202.80  
  Purchase #5 $230.26   11.755%   $257.3271   $257.33   $257.35   $257.30  
  Purchase #6 $229.40   13.405%   $260.1511   $260.15   $260.15   $260.20  
  Purchase #7 $230.63   5.850%   $244.1219   $244.12   $244.10   $244.10  
  7 purchase totals = $1,054.21       $1,160.9054   $1,160.90   $1,160.90   $1,160.80