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 $83.44   11.201%   $92.7861   $92.79   $92.80   $92.80  
  Purchase #2 $112.45   12.821%   $126.8672   $126.87   $126.85   $126.90  
  Purchase #3 $161.70   11.729%   $180.6658   $180.67   $180.65   $180.70  
  Purchase #4 $165.90   9.223%   $181.201   $181.20   $181.20   $181.20  
  Purchase #5 $203.90   7.782%   $219.7675   $219.77   $219.75   $219.80  
  Purchase #6 $87.92   7.519%   $94.5307   $94.53   $94.55   $94.50  
  Purchase #7 $140.69   8.112%   $152.1028   $152.10   $152.10   $152.10  
  7 purchase totals = $956.00       $1,047.9211   $1,047.93   $1,047.90   $1,048.00