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 $29.40   11.654%   $32.8263   $32.83   $32.85   $32.80  
  Purchase #2 $245.88   12.536%   $276.7035   $276.70   $276.70   $276.70  
  Purchase #3 $220.37   12.771%   $248.5135   $248.51   $248.50   $248.50  
  Purchase #4 $78.52   12.333%   $88.2039   $88.20   $88.20   $88.20  
  Purchase #5 $110.78   8.771%   $120.4965   $120.50   $120.50   $120.50  
  Purchase #6 $183.31   12.248%   $205.7618   $205.76   $205.75   $205.80  
  Purchase #7 $52.27   3.700%   $54.204   $54.20   $54.20   $54.20  
  7 purchase totals = $920.53       $1,026.7095   $1,026.70   $1,026.70   $1,026.70