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 $244.27   6.658%   $260.5335   $260.53   $260.55   $260.50  
  Purchase #2 $56.81   6.514%   $60.5106   $60.51   $60.50   $60.50  
  Purchase #3 $73.72   7.424%   $79.193   $79.19   $79.20   $79.20  
  Purchase #4 $94.69   8.586%   $102.8201   $102.82   $102.80   $102.80  
  Purchase #5 $171.63   13.410%   $194.6456   $194.65   $194.65   $194.60  
  Purchase #6 $194.26   6.165%   $206.2361   $206.24   $206.25   $206.20  
  Purchase #7 $107.29   7.731%   $115.5846   $115.58   $115.60   $115.60  
  7 purchase totals = $942.67       $1,019.5235   $1,019.52   $1,019.55   $1,019.40