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 $93.74   6.777%   $100.0928   $100.09   $100.10   $100.10  
  Purchase #2 $167.84   6.169%   $178.194   $178.19   $178.20   $178.20  
  Purchase #3 $182.45   6.700%   $194.6742   $194.67   $194.65   $194.70  
  Purchase #4 $106.69   3.466%   $110.3879   $110.39   $110.40   $110.40  
  Purchase #5 $181.38   12.147%   $203.4122   $203.41   $203.40   $203.40  
  Purchase #6 $165.57   7.580%   $178.1202   $178.12   $178.10   $178.10  
  Purchase #7 $200.84   10.443%   $221.8137   $221.81   $221.80   $221.80  
  7 purchase totals = $1,098.51       $1,186.6950   $1,186.68   $1,186.65   $1,186.70