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 $32.47   3.517%   $33.612   $33.61   $33.60   $33.60  
  Purchase #2 $140.30   10.205%   $154.6176   $154.62   $154.60   $154.60  
  Purchase #3 $65.86   5.755%   $69.6502   $69.65   $69.65   $69.70  
  Purchase #4 $209.26   12.672%   $235.7774   $235.78   $235.80   $235.80  
  Purchase #5 $33.56   3.780%   $34.8286   $34.83   $34.85   $34.80  
  Purchase #6 $202.40   10.169%   $222.9821   $222.98   $223.00   $223.00  
  Purchase #7 $175.52   11.552%   $195.7961   $195.80   $195.80   $195.80  
  7 purchase totals = $859.37       $947.2640   $947.27   $947.30   $947.30