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 $226.87   10.540%   $250.7821   $250.78   $250.80   $250.80  
  Purchase #2 $95.36   7.707%   $102.7094   $102.71   $102.70   $102.70  
  Purchase #3 $243.97   11.639%   $272.3657   $272.37   $272.35   $272.40  
  Purchase #4 $77.82   10.331%   $85.8596   $85.86   $85.85   $85.90  
  Purchase #5 $142.37   6.446%   $151.5472   $151.55   $151.55   $151.50  
  Purchase #6 $88.48   9.313%   $96.7201   $96.72   $96.70   $96.70  
  Purchase #7 $122.48   10.751%   $135.6478   $135.65   $135.65   $135.60  
  7 purchase totals = $997.35       $1,095.6319   $1,095.64   $1,095.60   $1,095.60