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 $89.81   4.663%   $93.9978   $94.00   $94.00   $94.00  
  Purchase #2 $137.52   5.831%   $145.5388   $145.54   $145.55   $145.50  
  Purchase #3 $68.25   13.707%   $77.605   $77.61   $77.60   $77.60  
  Purchase #4 $33.58   6.495%   $35.761   $35.76   $35.75   $35.80  
  Purchase #5 $202.80   5.284%   $213.516   $213.52   $213.50   $213.50  
  Purchase #6 $198.94   8.633%   $216.1145   $216.11   $216.10   $216.10  
  Purchase #7 $50.96   5.288%   $53.6548   $53.65   $53.65   $53.70  
  7 purchase totals = $781.86       $836.1879   $836.19   $836.15   $836.20