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 $54.96   7.353%   $59.0012   $59.00   $59.00   $59.00  
  Purchase #2 $201.29   7.644%   $216.6766   $216.68   $216.70   $216.70  
  Purchase #3 $123.29   8.585%   $133.8744   $133.87   $133.85   $133.90  
  Purchase #4 $213.57   11.405%   $237.9277   $237.93   $237.95   $237.90  
  Purchase #5 $101.68   9.492%   $111.3315   $111.33   $111.35   $111.30  
  Purchase #6 $203.44   6.186%   $216.0248   $216.02   $216.00   $216.00  
  Purchase #7 $11.77   10.538%   $13.0103   $13.01   $13.00   $13.00  
  7 purchase totals = $910.00       $987.8465   $987.84   $987.85   $987.80