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 $88.89   10.753%   $98.4483   $98.45   $98.45   $98.40  
  Purchase #2 $153.93   7.403%   $165.3254   $165.33   $165.35   $165.30  
  Purchase #3 $35.83   3.832%   $37.203   $37.20   $37.20   $37.20  
  Purchase #4 $32.78   3.781%   $34.0194   $34.02   $34.00   $34.00  
  Purchase #5 $189.53   11.755%   $211.8093   $211.81   $211.80   $211.80  
  Purchase #6 $227.29   9.130%   $248.0416   $248.04   $248.05   $248.00  
  Purchase #7 $178.96   13.662%   $203.4095   $203.41   $203.40   $203.40  
  7 purchase totals = $907.21       $998.2565   $998.26   $998.25   $998.10