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 $96.39   10.815%   $106.8146   $106.81   $106.80   $106.80  
  Purchase #2 $89.66   13.391%   $101.6664   $101.67   $101.65   $101.70  
  Purchase #3 $128.97   11.331%   $143.5836   $143.58   $143.60   $143.60  
  Purchase #4 $226.95   10.476%   $250.7253   $250.73   $250.75   $250.70  
  Purchase #5 $205.84   8.549%   $223.4373   $223.44   $223.45   $223.40  
  Purchase #6 $97.27   12.179%   $109.1165   $109.12   $109.10   $109.10  
  Purchase #7 $80.43   13.369%   $91.1827   $91.18   $91.20   $91.20  
  7 purchase totals = $925.51       $1,026.5264   $1,026.53   $1,026.55   $1,026.50