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 $46.75   11.370%   $52.0655   $52.07   $52.05   $52.10  
  Purchase #2 $184.78   7.534%   $198.7013   $198.70   $198.70   $198.70  
  Purchase #3 $212.79   6.445%   $226.5043   $226.50   $226.50   $226.50  
  Purchase #4 $217.40   5.107%   $228.5026   $228.50   $228.50   $228.50  
  Purchase #5 $41.29   7.361%   $44.3294   $44.33   $44.35   $44.30  
  Purchase #6 $159.86   5.120%   $168.0448   $168.04   $168.05   $168.00  
  Purchase #7 $31.40   7.780%   $33.8429   $33.84   $33.85   $33.80  
  7 purchase totals = $894.27       $951.9908   $951.98   $952.00   $951.90