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 $59.46   6.467%   $63.3053   $63.31   $63.30   $63.30  
  Purchase #2 $129.52   12.625%   $145.8719   $145.87   $145.85   $145.90  
  Purchase #3 $156.97   7.874%   $169.3298   $169.33   $169.35   $169.30  
  Purchase #4 $230.44   7.142%   $246.898   $246.90   $246.90   $246.90  
  Purchase #5 $130.54   3.294%   $134.84   $134.84   $134.85   $134.80  
  Purchase #6 $105.90   12.183%   $118.8018   $118.80   $118.80   $118.80  
  Purchase #7 $145.62   12.492%   $163.8109   $163.81   $163.80   $163.80  
  7 purchase totals = $958.45       $1,042.8577   $1,042.86   $1,042.85   $1,042.80