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 $125.50   6.761%   $133.9851   $133.99   $134.00   $134.00  
  Purchase #2 $174.84   3.496%   $180.9524   $180.95   $180.95   $181.00  
  Purchase #3 $230.82   3.441%   $238.7625   $238.76   $238.75   $238.80  
  Purchase #4 $186.54   5.134%   $196.117   $196.12   $196.10   $196.10  
  Purchase #5 $37.52   6.206%   $39.8485   $39.85   $39.85   $39.80  
  Purchase #6 $10.46   9.605%   $11.4647   $11.46   $11.45   $11.50  
  Purchase #7 $214.58   13.735%   $244.0526   $244.05   $244.05   $244.10  
  7 purchase totals = $980.26       $1,045.1828   $1,045.18   $1,045.15   $1,045.30