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 $181.28   8.593%   $196.8574   $196.86   $196.85   $196.90  
  Purchase #2 $243.92   13.332%   $276.4394   $276.44   $276.45   $276.40  
  Purchase #3 $58.60   9.110%   $63.9385   $63.94   $63.95   $63.90  
  Purchase #4 $80.89   12.816%   $91.2569   $91.26   $91.25   $91.30  
  Purchase #5 $118.87   4.273%   $123.9493   $123.95   $123.95   $123.90  
  Purchase #6 $196.88   7.660%   $211.961   $211.96   $211.95   $212.00  
  Purchase #7 $87.84   6.355%   $93.4222   $93.42   $93.40   $93.40  
  7 purchase totals = $968.28       $1,057.8247   $1,057.83   $1,057.80   $1,057.80