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 $192.33   9.583%   $210.761   $210.76   $210.75   $210.80  
  Purchase #2 $92.61   8.713%   $100.6791   $100.68   $100.70   $100.70  
  Purchase #3 $182.51   11.702%   $203.8673   $203.87   $203.85   $203.90  
  Purchase #4 $53.45   12.173%   $59.9565   $59.96   $59.95   $60.00  
  Purchase #5 $181.27   7.120%   $194.1764   $194.18   $194.20   $194.20  
  Purchase #6 $91.41   4.771%   $95.7712   $95.77   $95.75   $95.80  
  Purchase #7 $80.65   4.826%   $84.5422   $84.54   $84.55   $84.50  
  7 purchase totals = $874.23       $949.7537   $949.76   $949.75   $949.90