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 $186.85   9.157%   $203.9599   $203.96   $203.95   $204.00  
  Purchase #2 $65.56   9.721%   $71.9331   $71.93   $71.95   $71.90  
  Purchase #3 $47.76   8.294%   $51.7212   $51.72   $51.70   $51.70  
  Purchase #4 $55.85   11.334%   $62.18   $62.18   $62.20   $62.20  
  Purchase #5 $83.99   13.205%   $95.0809   $95.08   $95.10   $95.10  
  Purchase #6 $120.50   12.778%   $135.8975   $135.90   $135.90   $135.90  
  Purchase #7 $203.93   12.826%   $230.0861   $230.09   $230.10   $230.10  
  7 purchase totals = $764.44       $850.8587   $850.86   $850.90   $850.90