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 $61.82   6.251%   $65.6844   $65.68   $65.70   $65.70  
  Purchase #2 $158.68   13.424%   $179.9812   $179.98   $180.00   $180.00  
  Purchase #3 $193.91   6.776%   $207.0493   $207.05   $207.05   $207.00  
  Purchase #4 $57.59   7.738%   $62.0463   $62.05   $62.05   $62.00  
  Purchase #5 $159.36   10.343%   $175.8426   $175.84   $175.85   $175.80  
  Purchase #6 $138.96   10.731%   $153.8718   $153.87   $153.85   $153.90  
  Purchase #7 $186.98   13.162%   $211.5903   $211.59   $211.60   $211.60  
  7 purchase totals = $957.30       $1,056.0659   $1,056.06   $1,056.10   $1,056.00