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 $55.84   6.861%   $59.6712   $59.67   $59.65   $59.70  
  Purchase #2 $20.34   8.434%   $22.0555   $22.06   $22.05   $22.10  
  Purchase #3 $134.75   12.781%   $151.9724   $151.97   $151.95   $152.00  
  Purchase #4 $230.98   11.121%   $256.6673   $256.67   $256.65   $256.70  
  Purchase #5 $145.84   5.175%   $153.3872   $153.39   $153.40   $153.40  
  Purchase #6 $204.79   5.863%   $216.7968   $216.80   $216.80   $216.80  
  Purchase #7 $84.64   10.784%   $93.7676   $93.77   $93.75   $93.80  
  7 purchase totals = $877.18       $954.3180   $954.33   $954.25   $954.50