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 $230.45   6.144%   $244.6088   $244.61   $244.60   $244.60  
  Purchase #2 $157.70   9.376%   $172.486   $172.49   $172.50   $172.50  
  Purchase #3 $182.78   7.837%   $197.1045   $197.10   $197.10   $197.10  
  Purchase #4 $169.74   6.749%   $181.1958   $181.20   $181.20   $181.20  
  Purchase #5 $170.96   11.114%   $189.9605   $189.96   $189.95   $190.00  
  Purchase #6 $28.96   9.575%   $31.7329   $31.73   $31.75   $31.70  
  Purchase #7 $91.84   12.771%   $103.5689   $103.57   $103.55   $103.60  
  7 purchase totals = $1,032.43       $1,120.6574   $1,120.66   $1,120.65   $1,120.70